and left for some hours. The insoluble matter is collected on a weighed
filter and washed with ether until the latter dissolves nothing further^ the
filter being then placed on a clock-glass, dried at 100° and weighed. 'The
total impurity (gelatine, lime soaps, etc.) in the fat is thus determined.
If account is to be taken also of the fat combined as lime soap, treatment
of the substance with ether is preceded by an hour's heating, with occasional
shaking, on the water-bath with 3-5 drops of concentrated hydrochloric
acid; the lime soaps having been decomposed in this way, the further
procedure is as described above.
3. Determination of the Ash.—10 grams of the fat are carefully
incinerated and the residue weighed. The ash of bone fat is composed of
calcium oxide and a little carbonate, with small quantities of calcium phos-
phate, alumina and ferric oxide.
4. Titer.—As with tallow, the titer of bone fat is given by the solidifying
point of the free fatty acids, this being determined as in the case of tallow
5. Acid and Saponification Numbers.—By the general methods,
7 and 8. The acidity is expressed as percentage of oleic acid.
6. Hydroxy-acids.—As in General Methods, 15.
7. Unsaponifiable Substances.—These may be estimated by saponi-
fying the fat with alcoholic potash and extracting the aqueous solution of
the soap with ether (see General Methods, 19).
8. Recognition of Bone Fat which has been extracted with Ben-
zine.—According to Gianoli,1 this may be effected as follows :
(a) The fat,is subjected to prolonged distillation with concentrated
calcium chloride solution ; where the fat has been extracted with benzine,
oily drops which are not soluble in soda float on the surface of the distillate.
(b) The fat is saponified with alcoholic sodium hydroxide, the alcohol
expelled, the fatty acids liberated and washed with water, and this water
treated in the hot with ammonia : turbidity indicates the use of benzine.
9. Test for American Bone Fat.2—To ascertain if a sample of bone
fat of American origin may be used without inconvenience for soap-making,
th e following test is recommended:
100 grams of the fat and 30 c.c. of water are well shaken in a
small steam-heated vessel with 20 grams of sulphuric acid (66° Baume),
the mass being afterwards heated and then left to stand : if the fat separates
sharply and rapidly, it may be regarded as of good quality, but if an emulsion
difficult to separate forms, the fat will give poor results and a bad yield of
Commercial bone fats may have somewhat varying characters and com-
position : the water content usually ranges from i to 3%, but may reach even
20% ; extraneous impurities vary from 0-5 to 3% and the ash also from 0-5
to 3%. The titer for good products is 36-44°, the acidity may exceed 50%,
and the unsaponifiable matters usually lie between 0-5 and 2%.
The permissible limits for good bone fats for soap-making are : impurities,
up to 3% (lime and magnesia soaps, iron, moisture, mucilaginous matter, higher
2nd. Sapon., 1909, p. 3.
2 Ind. Sapon., 1914, p. 102.her sufficient to dissolve the fatty matter in the cold,